This application is the national phase application under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/DE99/03770 which has an International filing date of Nov. 24, 1999, which designated the United States of America.
The invention relates to an operating shaft for operation of switching contacts in a multipole electrical power circuit breaker having levers, which project from a central shaft tube (which is intended to provide a rotating bearing) and which are composed of die-cast metal, for connecting the operating shaft to the switching contacts and to an energy store which operates the switching contacts. The invention also relates to a method for producing such an operating shaft.
An operating shaft has been disclosed in DE 197 27 853 C1. In order to simplify the production of relatively long operating shafts, such as those which are required for four-pole power circuit breakers and those with a high rated current, the cited document provides for relatively short operating shaft units to be coupled to one another. In contrast, it would appear to be advantageous if it were possible to provide integral operating shafts with identical characteristics for all sizes in a range of power circuit breakers, and which are produced using the same method. The invention is based on the object of providing an operating shaft having these characteristics.
According to the invention, the above object is achieved in that the shaft tube is formed by a section of a tubular semi-finished product which is composed of a metal which has a higher melting point than that of the levers which project from the shaft tube, and in that the levers are mounted on the shaft tube.
The invention combines with one another the advantages of operating shafts which are produced from prefabricated individual parts by soldering or welding, and those which are produced as die-cast parts in accordance with the cited DE 197 27 853 C1. The fitting of the levers to a shaft tube comprising a tubular semi-finished product allows operating shafts to be produced cost-effectively of any required length and with any required number of levers. The advantageous characteristics of the new operating shaft are thus related to the production of die-cast parts of smaller size than is the case according to the cited DE 197 27 853 C1. Among other factors, this considerably reduces the quality assurance effort.
Relatively short operating shafts, such as those which are required for power circuit breakers having a normal number of poles and with a low to medium rated current can be constructed, according to one refinement of the invention, in such a manner that all the levers are formed by an integral die-cast body, with sections of the die-cast body which enclose the shaft tube in the form of a casing being arranged between the levers. However, to produce long operating shafts, it may be better to form each lever as a unit with concentric projections adjacent to it on both sides. This allows there to be exposed sections of the tubular semi-finished product between the levers.
Should it be found that the fitting of a die-cast material to the tubular semi-finished product does not at the same time achieve a strength which is sufficient for transmitting the required forces, then suitable roughening, profiling or the arrangement of depressions in the semi-finished product can be used to improve the force fit. A good connection can in consequence be achieved with particularly low effort in that the tubular semi-finished product for the shaft tube is composed of steel and is at least externally electrochemically galvanized in conjunction with die-shaft zinc being used as the material for the levers.
An expedient method for producing operating shafts with the characteristics described above comprises the following steps:
provision of a shaft tube composed of a tubular semi-finished product,
provision of a split casting mold for at least one of the levers and concentric projections which extend in the axial direction of the semi-finished product on both sides of the lever,
positioning of the shaft tube in the casting mold with a sealed closure on the circumference of the shaft tube,
introduction of a molten liquid die-casting material into the casting mold in order to form the lever and the adjacent projections, which are concentric with respect to the shaft tube,
opening of the casting mold once the die-casting material has cooled down to a reasonable extent, and removal of the shaft tube with die-cast bodies, which are attached thereto and have at least one lever and adjacent sections in the form of casings.